Electronic amplifiers come in a variety of configurations and types. For example, the term “electronic amplifier” applies to a current-to-voltage (I-V) amplifier, a voltage-to-voltage (V-V) amplifier, a voltage-to-current (V-I) amplifier, and a current-to-current (I-I) amplifier. Electronic amplifiers receive an electronic input signal and produce an electronic output signal that corresponds to the input signal multiplied by a gain factor, which is some non-zero positive or negative value.
One well-known type of I-V amplifier is a transimpedance amplifier (TIA). TIAs are often used in optical transceiver modules. In optical transceiver modules, a photodiode receives an optical signal passing out of the end of an optical fiber and produces an electrical current signal, which is then input to a TIA. The TIA then converts the electrical current signal into an electrical voltage signal, which is then output from the TIA. Other electrical circuitry downstream of the TIA processes the electrical voltage signal to recover the data bits.
Optical transceiver modules are typically required to be robust in terms of jitter performance and power consumption. In order to improve jitter performance in optical transceiver modules, it is known to include bandwidth (BW)-enhancement circuitry that increases the BW of the TIA. BW-enhancement circuitry used for this purpose adds a zero to the frequency response of the TIA to compensate for the effect of a pole that exists in the frequency response of the TIA. This BW-enhancement circuitry may take many forms, but one well known example is a resistor-capacitor (RC) shunt circuit. The disadvantage of this type of BW-enhancement circuitry is that it often results in “peaking” of the frequency response of the TIA, i.e., an overshooting of the gain of the frequency response. In high-speed optical transceiver modules that utilize adaptive equalizers, peaking should be minimized or prevented because the input signal to the equalizer must generally be linear in order for the equalizer to properly perform equalization.
An important characteristic of an electronic amplifier is the gain-BW (GBW) product, which is the product of the BW of the amplifier and the gain at which the BW is measured. The GBW product for an amplifier is generally constant over the operating range of the amplifier when amplifier biasing is not changed. Thus, an increase in the gain of the amplifier is usually accompanied by a decrease in BW, and vice versa. One way to reduce peaking is to reduce the BW of the amplifier. However, simply reducing the BW of the amplifier is undesirable in many cases and is counter to the goal of providing BW enhancement.
Accordingly, a need exists for way to provide BW enhancement in an electronic amplifier while also preventing, or at least reducing, peaking of the frequency response of the amplifier.